Publications

General Publications

Introduction to the Task 39 Info SheetsJuly 2015 - PDF 0.15MB - Posted: 2015-07-09By: Michael Koehl, Sandrin Saile, Fraunhofer ISETask 39 ”Polymers for Solar Thermal Applications“ of the International Energy Agency’s Solar Heating and Cooling Programme (IEA SHC) was a joint endeavor by polymer and solar thermal experts from industry and research. It started in 2006 with a variety of studies on polymeric materials’ suitability for the application in solar heating components. Investigations on novel designs that allow for alternative materials were elaborated as well as accompanying studies on the cost-reduction potential resulting from the efficient combination of material and product design.

Position Paper: Polymeric Materials for Solar Thermal ApplicationsIEA SHC Task 39: Position PaperJune 2015 - PDF 0.28MB - Posted: 2015-07-16This position paper describes the current state of the art for polymeric materials in solar thermal applications, shows the potential of polymers in solar thermal applications, and encourages further R&D activities. The major advantages of using polymeric materials in solar thermal systems are economical aspects, especially when taking into account the increasing solar thermal market and increasing raw material prices for metals. Although the cost of materials per mass unit might often be put forward as a major advantage of polymers relative to metals in conventional collectors, the entire picture is more complex. Many successful applications of polymeric materials in solar thermal systems that perform equally well or better in terms of conventional energy savings, reduction of materials, as well as production, transport, installation and/or end-user costs have been demonstrated.

Market and cost effects for polymeric solar thermal collectorsIEA-SHC Task 39 INFO Sheet A1May 2015 - PDF 0.35MB - Posted: 2015-05-24By: Andreas Piekarczyk, Karl-Anders WeissTalking about polymeric collectors, the reduction of production costs is one main argument for the use of polymeric materials instead of metals. This cost advantage can be split into two categories: lower material costs of the polymeric materials on the one hand and lower manufacturing costs on the other hand. Comparing just the prices for raw materials per kilogram is not sufficient and only little can be said about the saving potential of polymeric materials. In the here presented manner, using some assumptions, a detailed analysis of the cost effects of polymeric materials for the use in solar thermal applications can be performed.

100 Percent Renewable Energy Scenarios – Relevance of Plastics for Solar Thermal TechnologiesIEA-SHC Task 39 INFO Sheet A2May 2015 - PDF 0.35MB - Posted: 2015-05-24By: Klaus Holzhaider, Gernot M. Wallner, Harald Kicker, Reinhold W. Lang, Robert HausnerIn order to estimate the future demand for polymeric materials in solar thermal systems, the Institute of Polymeric Materials and Testing at JKU Linz (AT) and the AEE-Institute for Sustainable Technologies in Gleisdorf (AT) analyzed global and European scenarios that aim at a 100% renewable energy supply by 2050. Those scenarios were compared to European market scenarios established by ESTIF (European Solar Thermal Industry Federation). Based on these scenarios the resulting polymeric material demand until 2050 was calculated, and the results were compared to the potential development of the total global oil reserves and plastics production.

Task 39 Final ReportPresentation at SHC 2014 in Beijing ChinaOctober 2014 - PDF 1.21MB - Posted: 2014-10-16By: Dr. Michael KohlTask Objectives:- Assessment of the applicability and the cost reduction potential of polymeric materials for solar thermal systems - Novel polymer based designs- Evaluation of less expensive materials- Assessment of durability and reliability- Promote increased confidence in the use of these products - Development and application of appropriate testing and certification methods - Identification of less expensive manufacturing processes

Task 39 Highlights 2013Polymeric Materials for Solar Thermal ApplicationsFebruary 2014 - PDF 0.18MB - Posted: 2014-03-03One of the greatest challenges of the 21st century is to secure sustainable and save energy supply and to considerably reduce CO2 emissions and the potential serious consequences of climate change. The challenging goals with regard to the contributions of renewable energies cannot be obtained without a considerable growth of the solar thermal markets worldwide. Therefore, reliable, efficient and cost-competitive system components are required in large quantities. Today solar thermal collectors mainly consist of glass and metals whereas especially market prices for metals are subject to big fluctuations.

These issues demand the introduction of new materials, of which polymers seem to have a strong preference with regard to mass-production techniques, new design freedom, cost- and weight reduction.

Task 39 Highlights 2012January 2013 - PDF 0.1MB - Posted: 2013-02-10One of the greatest challenges of the 21st century is to secure sustainable and save energy supply and to considerably reduce CO2 emissions and the potential serious consequences of climate change. The challenging goals with regard to the contributions of renewable energies cannot be obtained without a considerable growth of the solar thermal markets worldwide. Therefore, reliable, efficient and cost-competitive system components are required in large quantities. Today solar thermal collectors mainly consist of glass and metals whereas especially market prices for metals are subject to big fluctuations.

Polymeric Materials for Solar Thermal ApplicationsDecember 2012 - Posted: 2012-11-26Editor: Michael Koehl, Michaela Georgine Meir, Philippe Papillon, Gernot M. Wallner, Sandrin Saile--- Bridging the gap between basic science and technological applications, this is the first book devoted to polymers for solar thermal applications. Clearly divided into three major parts, the contributions are written by experts on solar thermal applications and polymer scientists alike. The first part explains the fundamentals of solar thermal energy especially for representatives of the plastics industry and researchers. Part two then goes on to provide introductory information on polymeric materials and processing for solar thermal experts. The third part combines both of these fields, discussing the potential of polymeric materials in solar thermal applications, as well as demands on durability, design and building integration. With its emphasis on applications, this monograph is relevant for researchers at universities and developers in commercial labs.ISBN: 978-3-527-33246-5

Subtask A: Information

A1: State of the Art

Polymeric solar collectors and recyclingIEA-SHC Task 39 INFO Sheet A7May 2015 - PDF 0.31MB - Posted: 2015-05-24By: Michael Feuchter, Katharina ReschToday recycling has become one of the key topics in the last years because of the increasing amount of waste and the waste itself is already an important resource of raw material. The amount of polymeric waste has increased significantly over the last decades, especially. As a consequence different recycling options for polymeric materials were established which are outlined in the following. Subsequently challenges and opportunities concerning recycling of polymeric solar collectors are discussed.

Task 39 Exhibition – Assembly of Polymeric Components for a New Generation of Solar Thermal Energy SystemsEnergy Procedia, Volume 48, 2014, Pages 130–136March 2014 - Posted: 2014-04-08By: M. Koehl, Sandrin Saile, Andreas Piekarczyk, Stephan FischerEditor: Andreas HäberlePublisher: Elsevier Ltd.--- IEA SHC Task 39 is dedicated to the development, optimization and deployment of materials and designs for polymer based solar thermal systems and components. To increase the confidence in polymeric solar thermal applications, Task 39 actively supports international research activities and seeks to promote successful applications and state-of-the-art products. For the SHC conference 2013, different polymeric components suitable for domestic hot water preparation and space heating were singled out for an exhibition. Promising polymeric collectors, air collectors, thermosiphons, storage tanks and other components from industrial partners all over the world were brought to Freiburg and assembled at the Fraunhofer-Institute for Solar Energy Systems ISE. The resulting SHC Task 39 Exhibition of polymeric components shows the feasibility of all-polymeric solar thermal systems and highlights their potential, especially as scalable and modular applications for building integration or as export products to sunny regions.

A2: Taskforce on Total Cost Accounting Approach / LCA

Life cycle analysis for polymeric solar thermal collectorsIEA-SHC Task 39 INFO Sheet A3May 2015 - PDF 0.37MB - Posted: 2015-05-24By: Regine WeissWhen developing new solar collectors with novel materials, the reduction of their environmental impact should be considered. In this context, several studies were published analyzing the environmental impact through polymeric materials and comparing them with conventional metal based collectors and systems by using life cycle analysis methodologies.

Evaluation of thermosiphon systems by adopting a total cost accounting approachIEA-SHC Task 39 INFO Sheet A4May 2015 - PDF 0.41MB - Posted: 2015-05-24By: Bo Carlsson, Michaela Meir, John Rekstad, Andreas Piekarczyk, Regine Weiß, Dieter Preiß,To assess the suitability of polymer based solar thermosiphon systems three polymeric systems under development have been selected and compared with thermosiphon systems in which traditional materials like metals were used. For the comparison, a total cost accounting approach is adopted, which involves the analysis of differences in thermal performance, end-user investment costs, operation and maintenance (O&M) costs, reliability and long-term performance, climatic and environmental performance in relation to the costs of the polymeric systems versus those of the traditional ones.

A total cost perspective on use of polymeric materials in solar collectors - Importance of environmental performance on suitabilityApplied Energy 125 (2014) 10–20March 2014 - Posted: 2014-04-13By: Bo Carlsson, Helena Persson, Michaela Meir, John RekstadPublisher: Elsevier Ltd.--- To assess the suitability of solar collector systems in which polymeric materials are used versus those in which more traditional materials are used, a case study was undertaken. In this case study a solar heating system with polymeric solar collectors was compared with two equivalent but more traditional solar heating systems: one with flat plate solar collectors and one with evacuated tube solar collectors. To make the comparison, a total cost accounting approach was adopted. The life cycle assessment (LCA) results clearly indicated that the polymeric solar collector system is the best as regards climatic and environmental performance when they are expressed in terms of the IPPC 100 a indicator and the Ecoindicator 99, H/A indicator, respectively. [...]

A3: Taskforce on Standards, regulations and guidelines

Standards, Certification and RegulationsIEA-SHC Task 39 INFO Sheet A5May 2015 - PDF 0.31MB - Posted: 2015-05-24By: Stephan Fischer,To ensure the quality of the products in the rapidly growing solar thermal market, national and international standards for solar collectors, hot water stores and complete thermal solar systems have been established. In these standards, basic requirements for products as well as testing methods for the verification of these requirements are specified. Furthermore, test methods for the determination of the thermal performance are standardized. The target groups for the standards are manufactures and planners as well as testing institutes for thermal solar systems and components.

A4: Database of successful architectural integration

Architecturally appealing solar thermal systems - A marketing tool in order to attract new market segmentsIEA-SHC Task 39 INFO Sheet A6May 2015 - PDF 0.38MB - Posted: 2015-05-24By: Ingvild SkjellandArchitectural integration is a major issue in the development and dissemination of solar thermal technology. Unfortunately, the architectural quality of integrated solar thermal systems in many existing buildings is poor, which often discourages potential new users. Because solar thermal systems are relatively large in relation to the building envelope, the architectural quality of their integration has a major impact on the visual quality of the building. This should, together with the fact that public acceptance of solar energy to a high extent depends on the quality of the architectural integration, stimulate and motivate a much stronger focus on making solar thermal systems visually appealing– something people really would want to put on their houses and something architects would want to implement in their design of new buildings.

Online Database: Architectural Integration of Solar Thermal Energy SystemsTask 39January 2014 - Posted: 2007-10-26By: Ingvild Skjelland et. al.--- This database presents a range of buildings where solar thermal energy systems have been successfully integrated in the architecture. The core element of a solar thermal installation is solar collectors that convert the energy in sunlight directly into usable heat. These collectors can be aesthetically integrated with the building envelope or they can be mounted onto a building. Solar thermal installations have high energy capacity, and end users therefore benefit of an attractive pay back on their investment.

Towards an improved architectural quality of building integrated solar thermal systems (BIST)Solar Energy 81 (2007) 1104–1116June 2007 - Posted: 2014-01-26By: M.C. Munari Probst, C. Roecker--- Architectural integration is a major issue in the development and spreading of solar thermal technologies. Yet the architectural quality of most existing building integrated solar thermal systems (BIST) is quite poor, which often discourages potential new users. In this paper, the results of a large web survey on architectural quality, addressed to more than 170 European architects and other building professionals are presented and commented ...

Subtask B: Collectors

B1: Collectors

Performance requirements (general)IEA-SHC Task 39 INFO Sheet B1May 2015 - PDF 0.43MB - Posted: 2015-05-24By: T. Ramschak, D. PreißA crucial aspect of using polymeric materials in solar thermal systems is the exact knowledge about the occurring loads especially for temperature and pressure changes. The limited thermal property in various polymers in comparison to the present primarily used materials (copper, aluminum or glass) in reference systems makes it inevitable to determine load profiles. In the framework of the national project SolPol investigations were made to create temperature and pressure load matrices for the main components of solar thermal systems. To achieve a broad knowledge-base, different applications (domestic hot water in single and multifamily houses, combi-systems) and systems concepts for the main climate zones of the world have been investigated. Furthermore, modified polymeric solar thermal systems with overheat protection (backcooling, ventilation, thermotropic layer) and without overheat protection (drain-back, thermosiphon) have been examined. Extended simulations form the basis to deliver load profiles for solar thermal systems based on polymeric materials. Building on the results (system efficiency) derived from reference systems, the accompanying INFO Sheets B2: “Thermal stress” and B3: “Pressure stress” give an overview about the performance requirements for the materials which will be investigated.

Performance requirements (thermal stress)IEA-SHC Task 39 INFO Sheet B2May 2015 - PDF 0.6MB - Posted: 2015-05-24By: T. Ramschak, D. PreißSolar thermal systems that reach the stagnation state will overheat, resulting in high temperature and pressure loads for the collector and the surrounding components. Depending on how well these loads can be limited without reducing the efficiency in normal operation, determines whether high performance polymers or low-cost engineering or commodity plastics can be used.

Performance requirements (pressure stress)IEA-SHC Task 39 INFO Sheet B3May 2015 - PDF 0.54MB - Posted: 2015-05-24By: T. Ramschak, D. PreißConventional system behavior during stagnation is well understood and measures to handle this state are known. Nevertheless for economically priced polymer collectors stagnation will be a considerable challenge caused by the high temperature and pressure stress during standstill times of the solar system. In closed systems the pressure development is directly related to the temperature development. Therefore measures to overcome this disadvantage have already been mentioned in the accompanying INFO Sheet B2: “Temperature stress”. Open drain-back systems offer the ability to reduce the pressure stress.

Performance Optimisation of Polymeric Collectors by Means of Dynamic Simulation and Sensitivity AnalysisEnergy Procedia, Volume 48, 2014, Pages 181–191March 2014 - Posted: 2014-04-13By: Christoph Reiter, Sebastian Brandmayr, Christoph Trinkl, Wilfried Zörner, Victor I. HanbyEditor: Andreas HäberlePublisher: Elsevier Ltd.--- A dynamic flat-plate collector model for parametric sensitivity studies on polymer-based collector designs was developed. Validation using experimental results of conventional flat-plate collectors showed satisfying results especially regarding the calculation of individual part temperatures of a collector. The model was used to predict system efficiency as well as individual part temperatures in order to analyse a polymeric collector approach in comparison to a conventional collector. The simulation results showed that the fractional energy savings of systems with conventional flat-plate collectors cannot be reached with the analysed polymeric collector approach. Also the stagnation temperatures of more efficient approaches are too high for low-cost polymeric materials. The exemplary analysis of annual temperature loads of the backside insulation for different approaches proved the necessity of careful collector design aiming at temperature reduction for all individual collector parts.

B2: Systems

Fully Polymeric Thermosiphon SystemIEA-SHC Task 39 INFO Sheet B7May 2015 - PDF 0.41MB - Posted: 2015-05-24By: Andreas Piekarczy, Karl-Anders WeißWhile the development of fully polymeric collectors is proceeding very well, one of the major questions to address is the integration of polymeric collectors into existing systems. Considering the large number of thermosiphon systems sold worldwide, in many regions the focus should be on the development of costefficient thermosiphon systems. Comparing the actual market situation, the requirements on a thermosiphon system from the consumers point of view can be summarized: low investment costs, small systems for easy modular expansion and direct usability.

Thermal loads at components of state-of-the-art flat-plate collectorsIEA-SHC Task 39 INFO Sheet B9May 2015 - PDF 0.66MB - Posted: 2015-05-24By: Christoph ReiterApart from the maximum absorber temperature according to DIN EN ISO 9806 (2014), the thermal loads inside solar-thermal collectors are widely unknown. However, the use of cost-effective polymers requires a detailed knowledge about the thermal conditions the collector components are facing. Therefore, a conventional solar-thermal system integrated in a four person one-family house was analyzed in a fieldtesting (cf. Reiter et al. 2010). The house was equipped with a solar hot water and space heating system with 20m² of standard flat-plate collectors.

Polymeric solar heating systems Building integration and scalability of componentsIEA-SHC Task 39 INFO Sheet B13May 2015 - PDF 0.52MB - Posted: 2015-05-24By: Michaela MeirPolymeric materials for solar thermal applications open the way for new processing techniques that can provide modular and scalable solutions for solar thermal collectors and system components. During the Subtask B Industry Workshop at the 15th SHC Task 39 Experts Meeting in March 2013 in Mallorca, participants investigated which products could be found in the market. In a brainstorming session, experts examined how various scalable polymeric solar thermal components could be combined into a complete system and how the system could be presented to a broad professional audience.

Ideas for design and manufacturing of plastic storage tanksIEA-SHC Task 39 INFO Sheet B14May 2015 - PDF 0.33MB - Posted: 2015-05-24By: Michael Plaschkes, Kibutz MagenIn the last years plastic solar collectors have been developed and manufactured by various companies. Plastic pipes are used in these solar systems (PP, PEX, CPVC) but storage tanks are still mainly metallic. This info sheet presents some ideas for manufacturing low cost thermoplastic pressure storage -tanks for DHW solar systems.

Developing plastic-based solar collectors for the volume marketIEA-SHC Task 39 INFO Sheet B15May 2015 - PDF 0.39MB - Posted: 2015-05-24By: Robert Buchinger and Max WesleRecent estimates have shown a steadily rising need for solar collector panels worldwide, from 10 to 15 percent annually. By 2020 the annual demand for collector surface is thought to be around 200 to 400 million square meters. This demand will be met with great difficulty only, if at all, when relying on conventional aluminum or copper panels. Materials for traditional collector panels are scarce and, therefore, too expensive to produce or sell collectors as an affordable mass product. Sunlumo’s R&D is geared to bridge this gap between the two poles – of a sufficient raw material supply on the one hand and of low prices for the volume market on the other. Their R&D is thus focused on innovative technologies, new materials such as polymers, and manufacturing options for the mass market.

AventaSolar collector systemIEA-SHC Task 39 INFO Sheet B16May 2015 - PDF 0.6MB - Posted: 2015-05-24By: John RekstadThe motivation for the development of the AventaSolar concept was to offer architecturally appealing and cost competitive solutions for solar thermal energy production to the end user.

UNISOL – universal solar system for pre-heating waterIEA-SHC Task 39 INFO Sheet B17May 2015 - PDF 0.37MB - Posted: 2015-05-24In any solar thermal system, from the absorption, accumulation and distribution sub-systems, accumulation is the one that defines the principles and controls the other two and thus, the overall efficiency of the system. From this assumption, the Unisol project aims to develop an integrated set of R&D activities to design a universal, innovative, independent and intelligent system that manages the accumulation of heat that is capable of using almost any solar collector. This system is intended for pre-heating domestic hot water (DHW) as well as for low-temperature space heating, and also to simplify integrated systems (IS) for the support of individual subsystems in multifamily housing buildings. The project introduces several new peculiarities, such as its unique principles of universality and integration inside and outside of buildings and a reversible heat-exchanger circuit. The main promoter is JPrior - Fábrica de Plásticos Lda, a private Portuguese company, Aveiro University and the National Laboratory of Energy and Geology (LNEG).

UNISOL – solar combistore evaluation and optimizationIEA-SHC Task 39 INFO Sheet B18May 2015 - PDF 0.34MB - Posted: 2015-05-24By: Ricardo Amorim, Jorge Facão, João C. Rodrigues, Maria João CarvalhoUNISOL is a national project aiming at the development of an innovative, autonomous and intelligent universal system for management and accumulation of solar heat that can practically use any solar collector in the market. The system will simultaneously pre-heat domestic water (DHW) and space heating (SH). The main component is a combistore which includes a two-way heat exchanger.

Polymeric Solar Collectors or Heat Pump? – Lessons Learned from Passive Houses in OsloVolume 48, 2014, Pages 914–923March 2014 - Posted: 2014-04-13By: Michaela Meir, Espen Murtnes, Aylin Maria Dursun, John RekstadEditor: Andreas HäberlePublisher: Elsevier Ltd.--- Energy monitoring has been performed for two passive houses in Oslo during 2012-2013. One house is heated by a solar heating system, the other with an air-to-water heat pump. The objective has been to investigate the need for additional energy supply in order to provide the required indoor comfort and prepare domestic hot water. If corrected for differences in domestic hot water consumption and indoor temperature the two houses require almost equal amounts of auxiliary energy. The solar energy gain would increase significantly if the solar collectors were placed more appropriate, with less shading due to neighboring buildings and vegetation. Both heating technologies could improve performance with minor system adaptations. It was shown that solar thermal heating can compete with heat pump techology even for locations as far north as Oslo, Norway.

Subtask C: Materials

C1: Multi-Functional Polymeric Materials

Polypropylene absorber materialsIEA-SHC Task 39 INFO Sheet C1May 2015 - PDF 0.4MB - Posted: 2015-05-24By: Gernot M. Wallner, Markus PovaczPolypropylene (PP) grades offer a high potential for use in solar thermal absorbers, in particular for flat plate collectors with adequate overheating control. For unglazed swimming pool collectors blackpigmented PP grades are state of the art. PP absorber grades for glazed collectors have to be tailored according to the specific loadings conditions and performance requirements which are significantly dependent on collector and system type. In this info sheet a PP grade widely used for swimming pool absorbers and a novel PP grade investigated within the collaborative research project SolPol-2 are evaluated as to their applicability for glazed collectors with full overheating protection.

Overheating protection thermotropic layerIEA-SHC Task 39 INFO Sheet C3May 2015 - PDF 0.31MB - Posted: 2015-05-24By: Katharina Resch, Andreas Weber, Dieter P. GruberIn recent years thermotropic overheating protection glazings are in focus of interest both, in solar thermal collector technology and architectural design of buildings. A thermotropic glazing changes its light transmittance from highly transparent to light diffusing upon reaching a certain threshold temperature autonomously and reversibly. Among different thermotropic systems, especially thermotropic systems with fixed domains (TSFD) are considered to have the highest potential for practical application. In TSFD scattering domains are embedded in a polymer matrix, which exhibit a sudden change of the refractive index upon reaching the threshold temperature. At low temperatures the layer is translucent, as the refractive indices of matrix and domain are almost equal. If the difference of the refractive index of both components increases due to warming up to a determined temperature (switching threshold) the thermotropic film turns opaque

TISS coating as added value for polymeric solar absorberIEA-SHC Task 39 INFO Sheet C4May 2015 - PDF 0.35MB - Posted: 2015-05-24By: Ivan JermanPolymer based solar collectors are one of the important parts of modern architecture. Market demands are oriented to the colored absorbers to fulfil the demand of architects and integrate the collectors in new buildings. One of the options for production of colored collectors is usage of the Thickness Insensitive Spectrally Selective (TISS) paints. TISS paints are tailor-made, multifunctional materials based on a variety of organic macromolecules and functional and processing additives. The material aspects of the colored TISS paint coatings are focusing on pigments, metallic and metallized flake pigments and polymeric resin binders used for the production of solar paint coatings with the help of dispersant molecules in order to achieve uniform distribution of the finely ground pigment particles in the polymeric resin binder. An important prerequisite for the successful selection and use of pigments in solar-thermal systems is the usage of high absorptivity pigments with their high loading in combination with the low thermal emitting binder.

Bioplastics for solar collector componentsIEA-SHC Task 39 INFO Sheet C5May 2015 - PDF 0.3MB - Posted: 2015-05-24By: Katharina Resch, Andrea Klein, Gernot OreskiNumerous research and development activities carried out by renowned research facilities and the global players in the polymer and solar industry – presented and discussed also within the framework of IEA SHC Task 39 – demonstrate that polymers are the materials of choice for next generation solar thermal systems. In addition to classical polymers made from petrochemical resources bioplastics (i.e. polymers based on renewable resources and/or biodegradable polymers) have been introduced as a sustainable and seminal alternative.

Tool box for basic characterization of plasticsIEA-SHC Task 39 INFO Sheet C6May 2015 - PDF 0.51MB - Posted: 2015-05-24By: Gernot M. Wallner, JKU LinzPlastics are tailor-made, multifunctional materials based on a variety of organic macromolecules and functional and processing additives. An important prerequisite for the successful selection and use of plastics in solar-thermal systems is the comprehensive definition and description of application-relevant loading profiles and the deduction of property requirements. For specified plastics grades reproducible material quality has to be controlled and assured. In this info sheet a tool box for the basic characterization of plastics for solar-thermal systems is described. Relevant features and properties are exemplarily depicted for absorber materials based on polyphenyleneoxide (PPO) and polyphenylenesulfide (PPS).

Case study: Accelerated UV-AgingIEA-SHC Task 39 INFO Sheet C7.1May 2015 - PDF 0.39MB - Posted: 2015-05-24By: Andreas Piekarczyk, Karl-Anders WeißPolymeric materials for solar thermal applications have to be tested thoroughly before they can be used for the construction of novel collectors. Used as absorbers, glazing or framing, just to mention a few applications, polymers are exposed to a broad variation of different environmental influences which may affect physical and mechanical properties of the materials and limit their service life time. Three major environmental influences, so called degradation factors are: temperature, UV radiation and humidity. One of these factors, the UV radiation, is of great impact on all organic macromolecules, like polymeric materials.

The Art of Stabilization – Analytical Evaluation of Stabilizer SystemsIEA-SHC Task 39 INFO Sheet C7.2May 2015 - PDF 0.36MB - Posted: 2015-05-24By: Susanne Beißmann, JKU LinzWithout proper stabilization, polymers are susceptible to degradation caused by reactions with oxygen or UV-light, which lead to undesirable changes in the properties of the polymer. A stabilization system is normally added to the polymeric material, which is responsible for maintaining mechanical properties like strength and toughness. Unfortunately, it is not yet fully clear which combination of stabilizers provides the best performance for a specific application. Furthermore, interactions between different stabilizer classes have to be carefully investigated as they may lead to exploitable synergistic or avoidable antagonistic effects.

Polymeric Liner Materials for Hot Water Heat StoragesIEA-SHC Task 39 INFO Sheet C7.3May 2015 - PDF 0.36MB - Posted: 2015-05-24By: Klemens Grabmayer, JKU LinzHot water heat storages are important components of solar thermal systems. Various polyolefin-based material grades are material candidates to serve as liners in hot water heat storages. In order to fulfil the requirements, characterization of the aging behavior is indispensable for material selection.

Case Study: Twin wall sheet testingIEA-SHC Task 39 INFO Sheet C7.4May 2015 - PDF 0.38MB - Posted: 2015-05-24By: Andreas Piekarczyk, Alyin DursonWhen using polymeric materials for solar thermal flat plate collectors, one distinct difference in physical properties compels us to reinvent the absorber design. Due to the low thermal conductivity of polymeric materials, the absorber, in order to prevent local overheating and to increase the collectors’ efficiency, needs water contact throughout the whole surface. In general only few absorber designs fulfill this requirement, e.g. thin plastic film absorbers, tube absorbers or twin wall sheets. The latter two are in the focus of recent development due to mechanical stability and economic efficiency. In order to investigate changes in the mechanical properties of the used materials as closely to the product as possible suitable mechanical testing methods need to be applied. For pipes, methods to test different mechanical loads already exist, but for twin wall sheets none of these can be applied.

Thermotropic Overheating Protection Glazings: Effect of Functional Additives and Processing Conditions on Light-Shielding EfficiencyJournal of Polymer Engineering 2014 Vol: 34(2):161-172. DOI: 10.1515/polyeng-2013-0275February 2014 - Posted: 2014-04-27By: Weber, A., Resch, K.Editor: Grizzuti, NinoPublisher: Walter de Gruyter GmbH--- Within this study, the effect of functional additives and processing conditions on the overheating protection performance of thermotropic systems with fixed domains (TSFD) for overheating protection purposes was evaluated. The focus was on improving the overheating protection performance of a prototype TSFD based on a UV curable acrylate resin by optimization of the material constitution (addition of functional additives like surfactants and nucleating agents) and the processing conditions (temperature conditions during manufacturing, annealing). For the evaluated system, an effect of the nucleating agent on the overheating protection performance was ascertained. Furthermore, omission of an annealing step improved the overheating protection performance slightly.ISBN: ISSN (Online) 2191-0340

A Model of the Optical Properties of a Non-absorbing Media with Application to Thermotropic Materials for Overheat Protection,Energy Procedia 30 (2012) 116-124November 2012 - Posted: 2014-01-26By: A. Gladen, J.H. Davidson, S, Mantell, J. Zhang, Y. XuPublisher: Elsevier Ltd.--- Thermotropic materials offer the potential to provide overheat protection for polymer absorbers. These materials are composed of a matrix material in which a second material, referred to as the scattering domain, is dispersed. Temperature control is accomplished by a reduction in transmittance at a desired temperature corresponding to the phase change temperature of the scattering domain. The phase change is accompanied by a change in refractive index. This paper describes a numerical model to predict the transmittance and reflectance of a polymer based thermotropic material as a function of the relative index of refraction m between the matrix and scattering domains, the scattering domain size and volume fraction fv, and the sheet thickness ...

Thermotropic glazings for overheating protectionEnergy Procedia 30 (2012) 471-477November 2012 - Posted: 2014-01-26By: A. Weber, K. ReschPublisher: Elsevier Ltd.--- In this paper, the effect of material composition on the overheating protection performance of thermotropic systems with fixed domains (TSFD) is studied. Several thermotropic layers were formulated by variation of both, matrix material and thermotropic additive. Refractometry was applied in order to obtain refractive index data as a function of temperature of all material constituents and to screen wether material combinations are promising to formulate or not. Investigations concerning optical properties, switching temperature and switching process were carried out applying UV/Vis/NIR spectrometry. Morphological analysis was conducted with a Scanning Electron Microscope (SEM). Several TSFD showed reasonable light-shielding efficiency. Nevertheless further optimization of scattering domain size and shape is necessary to improve the light shielding performance.

Coil-coated spectrally selective coatings on copper or aluminium with pigments modified by aminosilanesWIPO Patent Application WO 2010/133693May 2010 - Posted: 2011-06-05By: Koželj M, Orel B, Jerman I, Steinbücher M, Vodlan M, Peros D.--- The invention relates to TSSS and TISS coatings applied by coil-coating onto substrates of copper or aluminum. Inorganic pigments functionalized by aminosilane are used for making paints, which after the coil-coating onto the substrate form the coatings. For the functionalization the pigment is dispersed in a solution of an aminosilane in a solvent or a mixture of a solvent and a binder without an addition of a non-aminosilane dispersing agent with or without subsequent grinding and use of 0.05-30 % of aminosilane on pigment. An aromatic, aliphatic, cycloaliphatic, ketone, ester, ether or alcohol compound or a mixture thereof can be used as the solvent. A silicone-polyester, polyurethane or fluoropolymer can be used as the binder.

Phase separated thermotropic layers based on UV cured acrylate resins – Effect of material formulation on overheating protection properties and application in a solar collectorSolar Energy (83) 9, pp. 1689-1697September 2009 - Posted: 2010-06-03By: Resch, K., Wallner, G.M. and Hausner, R.--- This paper focuses on the effect of material composition on the overheating protection properties of thermotropic systems with fixed domains for solar thermal collectors. Numerous functional layers were prepared by a variation of base resin (polyester-, epoxy- or urethane–acrylate) and of thermotropic additives (non-polar and polar waxes) as well as by additive concentration (5 and 7 wt%). A detailed investigation of optical properties, switching temperature and switching process was performed applying UV/Vis/NIR spectroscopy. Thermal transitions of both the thermotropic layers and the additives used were determined by Differential Scanning Calorimetry (DSC). The capability of the produced thermotropic layers to reduce stagnation temperatures in an all-polymeric flat plate collector was evaluated by theoretical modeling. The thermotropic layers showed a hemispheric solar transmittance between 76% and 87% in clear state. Above the switching threshold this transmittance changed by 1–16% to values between 62% and 85% ...

Adhesion and thermal stability of thickness insensitive spectrally selective (TISS) polyurethane-based paint coatings on copper substratesSolar Energy Materials and Solar Cells (93) 5, pp. 630-640May 2009 - Posted: 2010-06-03By: Kunic, R., Kozelj, M., Orel, B., Šurca Vuk, A., Vilcnik, A., Slemenik Perse, L., Merlini, D., Brunold, S.--- Thickness insensitive spectrally selective (TISS) paint coatings based on a polyurethane polymeric binder deposited on copper substrates were investigated to obtain information about their service lifetime. The degradation of TISS paint coatings was performed according to the methodology worked out within Task 10 of the IEA's Solar heating and the cooling programme. The activation energy (Ea) for the degradation process was derived from vibrational band changes of the polyurethane binder recorded in the infrared hemispherical reflectance spectra of TISS paint coatings exposed to different thermal loads. The results of the vibrational band analysis were correlated with cross-cut tests, showing that the coatings started to lose integrity at 190 °C but protected the copper substrate against oxidation perfectly even at 200 °C (15 days). An accelerated test procedure confirmed that TISS coatings could be safely used in solar collectors for at least 45 years.

Thermotropic layers for flat-plate collectors - A review of various concepts for overheating protection with polymeric materialsSolar Energy Materials and Solar Cells (93) 1, pp. 119-128January 2009 - Posted: 2010-06-03By: Resch, K. and Wallner, G.M.--- Within this paper a comprehensive review of the developments of thermotropic hydrogels, thermotropic polymer blends and thermotropic systems with fixed domains for overheating protection purposes is given. In addition, performance properties for thermotropic layers to prevent overheating in solar collectors are defined. The different thermotropic material classes are discussed as to their ability to meet these requirements. The review shows that thermotropic layers developed so far need to be adapted as to switching temperature and long-term stability for applicability in solar thermal collectors.

Spectroscopic investigations of phase-separated thermotropic layers based on UV cured acrylate resinsMacromolecular Symposia (2008)December 2008 - Posted: 2012-03-03By: K. Resch, G.M. Wallner, R.W. Lang--- In this paper spectroscopic techniques were adapted and applied to characterize the optical and morphological properties of thermotropic resins. Thermotropic films were prepared by variation of resin base and thermotropic additives. By UV/Vis/NIR spectroscopy the solar optical properties, the switching temperature, the switching process and the residual transmittance in the opaque state were determined. To control the sample temperature from ambient to 100?°C a conventional UV/Vis/NIR spectrophotometer equipped with an Ulbricht-sphere was adapted by a heating stage. Additive content, distribution and scattering domain size were characterized by Differential Scanning Calorimetry, Attenuated Total Reflectance spectroscopy and microscopic techniques ...Document Number: 265, 49-60

Property and performance requirements for thermotropic layers to prevent overheating in an all polymeric flat-plate collectorSolar Energy Materials and Solar Cells (92), pp. 614-620June 2008 - Posted: 2010-06-03By: Resch, K., Wallner, G.M. and Hausner, R.--- Within this study the potential of thermotropic layers to prevent overheating of an all-polymeric solar collector is evaluated by theoretical modeling. The investigations show that collector stagnation temperatures can be reduced to temperatures between 80 and 90 °C by using thermotropic layers either in the glazing or on the absorber. For overheating protection to a maximum temperature of 80–90 °C a residual solar transmittance of the thermotropic layer below 0.25 in the opaque state (>0.85 in clear state) is effectual. The required switching temperature is dependent on the collector configuration.

C3: Testing and Characterization of Polymeric Materials

Testing of Components for Solar Thermal Collectors in Respect of Saline AtmospheresEnergy Procedia, Vol. 48, 2014, 731-738March 2014 - Posted: 2014-04-13By: T. Kaltenbach, E.Klimm, T. Meier, M. Köhl, K.A. WeißEditor: Andreas HäberlePublisher: Elsevier Ltd.--- Typical components for solar thermal collectors like glazing materials, absorbers and reflectors are exposed to accelerated weathering tests to analyze their stability and behavior under different climatic conditions including a saline atmosphere. The samples are characterized before, during and after the tests with different methods, including FT-IR spectroscopy and microscopic technologies like AFM microscopy to measure the degradation on different scales and identify the processes taking place. In this article we focus on the solar reflector

Black pigmented polypropylene materials for solar absorbersEnergy Procedia 30 (2012) 438-445November 2012 - Posted: 2014-01-26By: M. Kurzböck, G.M. Wallner, R.W. LangPublisher: Elsevier Ltd.--- Polyolefin materials are of high relevance and interest for absorbers of solar thermal collectors with integrated overheating protection. In this work the effect of various black pigments (carbon black (CB) and carbon nanotubes (CNT)) on optical and mechanical properties of PP-RCT grades (Polypropylene-Random Copolymer with special crystalline structure (ß phase) for elevated temperature applications) is investigated. To meet the requirements of high absorbance in the solar wavelength range (> 90%) and enhanced mechanical properties at service temperatures up to 90°C for at least 10 years, black pigmented specimens are characterized in an unaged state by UV/Vis/NIR- spectrometry and tensile testing. The experimental results reveal ...

Fracture behavior of degraded polyethylene thin films for solar thermal applicationsEnergy Procedia 30 (2012) 783-792November 2012 - Posted: 2014-01-26By: H. Ge, G. Singh, S. MantellPublisher: Elsevier Ltd.--- Thin polymer films and tubes are under consideration as materials for use in roof top mounted solar thermal collectors. When polymer components are exposed to chlorinated water or UV light, degradation can lead to diminished mechanical performance and premature failure from rupture. In this paper, fracture toughness and crack growth of degraded polyethylene (MDPE) are investigated. Thin film PE samples (0.3mm thick) are degraded through exposure to 80°C chlorinated water (8 ppm chlorine) for up to 45 days ...

Aging tests of components for solar thermal collectorsEnergy Procedia 30 (2012) 805-814November 2012 - Posted: 2014-01-26By: T. Kaltenbach, M. Kurth, C. Schmidt, T. Meier, M. Köhl, K.A. WeißPublisher: Elsevier Ltd.--- Components for solar thermal collectors like glazing materials, absorbers and reflectors are exposed to outdoor weathering and accelerated weathering tests in order to analyze their stability and behavior under different climatic conditions. To measure the degradation on different scales and to identify the processes taking place, the samples are characterized before, during and after the tests with different methods, including FT-IR spectroscopy, contact angle measurement and microscopic technologies such as Atomic Force Microscopy (AFM).

Degradation model for an extruded polymeric solar thermal absorberSolar Energy Materials and Solar Cells (94) 6, pp. 1031-1037June 2010 - Posted: 2010-06-03By: Olivares, A., Rekstad, J., Meir, M., Kahlen, S. and Wallner, G.M.--- A mechanical test is used to characterize the ageing process of a polymeric solar absorber as a consequence of exposure to high temperature. Specimens from the polymeric absorber sheet were exposed to different temperature and time conditions. Specimens were then tested using mechanical indentation to evaluate the damage level produced. Based on these measurements, this work proposes a model to predict degradation of the polymeric solar absorber during their service life. Model predictions are compared with results from a polymeric absorber exposed to outdoor conditions during two years.

Aging behavior and lifetime modeling for polycarbonateSolar Energy, (84) 5, pp. 755-762May 2010 - Posted: 2010-06-03By: Kahlen, S., Wallner, G.M. and Lang, R.W.--- In this paper, polycarbonate (PC) as a material candidate for solar absorber applications is investigated as to the aging behavior at different temperatures in air and water. The aging conditioning was performed in air in the temperature range from 120 to 140 °C and in water between 70 and 95 °C. Tensile tests were performed on unaged and aged PC film specimens at ambient temperature using strain-to-break values as a performance indicator for the degree of aging. For PC the effect of aging was found to strongly depend on the ageing conditions ...

Aging behavior of polymeric solar absorber materials – Part 2: Commodity plasticsSolar Energy (8) 9, pp. 1577-1586May 2010 - Posted: 2010-06-03By: Kahlen, S., Wallner, G.M. and Lang, R.W.--- In this series of two papers, various polymeric materials are investigated as to their potential applicability as absorber materials for solar thermal collectors. Part 2 treats the aging behavior of semi-crystalline so-called “commodity” plastics (two types of crosslinked polyethylene (PE-X) and two types of polypropylene (PP)). The focus of the investigation is to study the aging behavior of these materials under maximum operating conditions (80 °C in water up to 16,000 h) and stagnation conditions (140 °C in air up to 500 h) typical for northern climate. The materials supplied or produced as polymer films were first characterized in the unaged state and then for different states of aging by differential scanning calorimetry (DSC), by size exclusion chromatography (SEC) and by mechanical tensile tests. DSC was applied primarily to obtain information on [...]

Aging behavior of polymeric solar absorber materials – Part 1: Engineering plasticsSolar Energy (8) 9, pp. 1567-1576April 2010 - Posted: 2010-06-03By: Kahlen, S., Wallner, G.M. and Lang, R.W.--- In this series of two papers, various polymeric materials are investigated as to their potential applicability as absorber materials for solar thermal collectors. The focus of the investigation is to study the aging behavior of these materials under maximum operating conditions (80 °C in water up to 16,000 h) and stagnation conditions (140 °C in air up to 500 h) typical for northern climate. The materials supplied or produced as polymer films were first characterized in the unaged state and then for different states of aging by differential scanning calorimetry (DSC), by size exclusion chromatography (SEC) and by mechanical tensile tests. Physical aging phenomena were studied by DSC, SEC analysis provided information on chemical degradation of the materials. In addition, physical and chemical aging were both analyzed via the small and large strain mechanical behavior. Part 1 of this paper series deals with the aging behavior of engineering plastics, including two amorphous polymers (a polyphenylene ether polystyrene blend (PPE + PS) and polycarbonate (PC)) and two semi-crystalline polymers (two types of polyamide 12 (PA12)).

Characterization of physical and chemical aging of polymeric solar materials by mechanical testingPolymer Testing, vol. 29, pp. 72-81February 2010 - Posted: 2010-06-03By: Kahlen, S., Wallner, G.M. and Lang, R.W.--- The potential of mechanical tensile testing to characterize aspects of physical and chemical aging of polymeric solar materials as films was investigated. For this purpose, two types of polymer films, one being a multi-phase amorphous material (blend of polyphenylene ether and polystyrene (PPE + PS)) the other being a crosslinked semi-crystalline material (polyethylene (PEX-1)), were exposed to water at 80 °C for up to 16,000 h prior to being tested mechanically at room temperature. The properties deduced from mechanical tests to indicate aging were the modulus of the films, characteristic for the small-strain behavior, and the values for strain-to-break, characteristic for the post-yield behavior and ultimate failure at large strains ...